Hi list,
My name is Brett Stottlemyer. I work for Ford Motor Company, and Ford has
graciously agreed to let us contribute some of the cool stuff we've developed
back to Qt. We aren't quite done with everything yet (still waiting on the
Corporate CLA), but I will be at Qt Contributors Summit in a week and a half to
discuss this and a 2nd project, and answer (hopefully a bunch) of good
questions.
I'd like to officially request a sandbox for: QQSM
What is it?
QQSM is the Qt QML State Machine. Simply put, it is a QML module to allow you
to create Qt State Machine Framework instances via the QML engine.
What need does this module solve?
QQSM makes it a lot easier to create state machines. You get all of the
benefits of the maturity of Qt's State Machine Framework, the ability to
introspect/debug the machine with tools like gammaray, but with a simplified
syntax and QML's runtime bindings. An example of the simplification? A guard
condition for a transition can use QML/javascript and use signal parameters in
deciding whether to trigger a transition - entirely in QML markup.
Detailed description
QQSM is basically a Domain Specific Language (in QML) for simplified
descriptions of State Machines. While the C++ State Machine Framework is
complete, it requires a lot of boilerplate code. The examples I've seen have
created numerous QSignalTransition derived classes, one for each boolean
condition required to test for a transition.
While QML already has a State type, this is not a complete, deterministic state
machine. This is an overly simplified state machine, in that it provides
little in terms of error checking or nested states.
The proposed QQSM module, on the other hand, provides BasicState (to not
conflict with existing State type), HistoryState and FinalState, plus
StateMachine, SignalTransition and TimeoutTransition types. The benefit of QML
for State Machines is much more than just having to write less code, though.
Two features of the QML engine are runtime processing of scripted code, and
dynamic Signal/Slot connections. Since all SignalTransition classes provide a
boolean result for eventTest(), a single C++ implementation was created that
uses a boolean property ("guard") for the eventTest result. This allows any
QML/Javascript expression that resolves to a boolean to be used. The dynamic
connections make is easy to bind onEntry and onExit signals to non-state
machine QObjects.
The end result is an environment that allows State Machines to be developed
rapidly and succinctly.
Hope you like the idea, and approve the sandbox area.
Looking forward to your thoughts!
Sincerely,
Brett Stottlemyer
Ford Motor Company
_______________________________________________
Development mailing list
[email protected]
http://lists.qt-project.org/mailman/listinfo/development
